Time Division Multiplexing (TDM) is a technique where multiple logical channels are multiplexed on a single physical channel. It operates by assigning fixed length time slots to different channels in a round robin fashion.
TDM Superchannels are a technique where a logical channel is assigned more than one of the round robin time slots. If data becomes available for a Superchannel after its first time slot has been processed in a round robin circuit, starting transmission of a new block of data in other than the first time slot assigned to the Superchannel may not be recognized as such by the receiver.